This invention relates to a stylet for use with a lead bearing an electrode for electrically connecting an organ inside a living animal body to an electrical device. Notwithstanding its various uses, this invention will be described for use as an endocardial pacing and sensing lead for connecting an artificial cardiac pacemaker to cardiac tissue.
Endocardial pacing and sensing leads of the type shown in U.S. patent application Ser. No. 839,062, filed Oct. 3, 1977, now U.S. Pat. No. 4,217,913 for a Body Implantable Lead With Protected Extendable Tissue Securing Means, for example, comprise one or more lengths of hollow, coiled wire conductor encased within a suitable insulating material, such as silicone rubber, that is substantially inert to body fluids and tissues, a hollow connector pin attached to the proximal end of each of the conductors, and an electrically conductive electrode at the distal end of each of the conductors adapted to be placed in contact with the endocardium of the patient. A lumen extends through each pin and the corresponding lengths of coiled wire conductor to the electrode at the distal ends thereof and receives a stiffening stylet of cylindrical corrosion resistant wire for imparting stiffness to the lead to facilitate its advancement through the venous system of the patient and into the apex of the right ventricle. With the stylet removed from the lead, the lead is very flexible and difficult to so advance. Further details of the construction and utility of such endocardial pacing leads may be obtained by reference to U.S. Pat. Nos. 3,348,584 and 4,046,151, as well as the above-identified pending application Ser. No. 839,062.
An improved cardiac pacing lead employing a rigid helix with a sharp tipped distal end adapted to be screwed into the endocardium is disclosed in co-pending U.S. patent application Ser. No. 839,062, which is assigned to Medtronic, Inc. The improved lead disclosed in that application can be lodged in and permanently secured to or removed from body tissue without the use of bulky sleeves or catheter introducers to protect the patient's veins and tricuspid valve from snagging on the sharp tip of the helix.
In the improved lead disclosed in Ser. No. 839,062, the tissue securing means is a helix with a piston member fixed to its proximal end and positioned in a chamber within the electrode body. A stylet having a knob at its proximal end is passed through a lumen in the lead which communicates with the opening in the proximal end of the lead body such that the distal end of the stylet which is shaped in the form of a screwdriver head, is engagable with a slot in the head of the piston means. The stylet may be rotated after the distal end of the lead is positioned near the endocardial tissue and when the stylet is rotated the piston means is caused to screw the helix out of the distal opening in the electrode lead and into the endocardial and myocardial tissue to secure the electrode.
The implantable lead of the present invention incorporates an improved stylet to increase the effectiveness in the placement of either the endocardial leads of the type disclosed in U.S. Pat. No. 4,046,151, or in the co-pending application Ser. No. 839,062. A feature of the present invention is the provision of a stylet adapted to be extremely flexible in the vicinity of the distal end of the lead to increase the flexibility of the lead without detracting from the ability of the lead to transmit torque from its proximal end to its distal end. The improved structure facilitates the transmission of torque by the stylet even when the stylet and lead are sharply bent. The improved structure also permits the stylet and lead to be used where it is necessary to pass them through a sharp bend during insertion. Additionally, the improved flexible stylet may be inserted with less chance of snagging the helical coil conductor of the lead and perforating either the lead or surrounding tissue. The improved structure also provides an improved screwdriver tip for inserting the electrode into the tissue into which it is to be lodged.